The present invention relates generally to a semiconductor device having a wiring substrate formed by using glass fabrics impregnated with resin. More particularly, the present invention relates to a semiconductor device in which pad electrodes formed on the wiring substrate and projected electrodes or bump electrodes of a semiconductor pellet are opposed and superposed, and the pad electrodes and the projected electrodes superposed on each other are pressed toward each other and heated to electrically couple the projected electrodes and the pad electrodes.
It is desired that portable type electronic circuit devices, such as a note type personal computer, a portable telephone and the like, are compact and lightweight. Therefore, the external size of each electronic component used in the portable type electronic devices is reduced by reducing the sizes of one or more electronic parts used in the electronic component. In other way, each electronic component is substantially downsized by increasing the mounting density of the electronic parts included in the electronic component although the external size of the electronic component is the same as before.
Also, each lead as an electrode for coupling the electronic component and an external circuit is shaped into a surface mountable form and, thereby, projection length of the lead is reduced. Further, each lead is replaced by a projection type electrode such that an external size of the electronic component can be reduced as small as possible. In this way, the electronic components are downsized.
As an example of such electronic components, a semiconductor device having a Chip Size Package (CSP) structure is generally used. In the semiconductor device having the CSP structure, a semiconductor pellet is flip-chip bonded on a wiring substrate and the semiconductor pellet and the wiring substrate are bonded by using resin.
With reference to the drawings, an explanation will be made on a conventional semiconductor device having the CSP structure. FIG. 3 is a side cross sectional view showing a schematic structure of a conventional semiconductor device having the CSP structure. The conventional semiconductor device 110 shown in FIG. 3 comprises a wiring substrate 104, and a semiconductor pellet 101 mounted on the wiring substrate 104. The semiconductor pellet 101 has a semiconductor substrate 102 and many projected electrodes 103 formed on one of the main surfaces of the semiconductor substrate 102. In the semiconductor substrate 102, a number of electronic elements (not shown in the drawing) are formed and wired internally to form circuits.
A wiring substrate 104 comprises an insulating substrate 105, pad electrodes 106 formed on one of the main surfaces of the insulating substrate 105, and electrodes 107 for external connection formed on the other of the main surfaces of the insulating substrate 105. The pad electrodes 106 are formed at locations corresponding to those of the projected electrodes 103 of the semiconductor pellet 101. The pad electrodes 106 are electrically coupled with the electrodes 107 for external connection via conductor patterns not shown in the drawing.
The projected electrodes 103 of the semiconductor pellet 101 are superposed on the pad electrodes 106 of the wiring substrate 104 and coupled therewith by soldering, pressure welding, thermal compression bonding or ultrasonic bonding. Thereby, the projected electrodes 103 and the pad electrodes 106 are electrically connected to each other. Also, the semiconductor pellet 101 and the wiring substrate 104 are bonded by resin 108.
Further, on each of the electrodes 107 for external connection, there is formed a solder ball 109. Each of the solder balls 109 is shaped into a spherical form by melting a solder on the electrode 107 for external connection.
In the semiconductor device 110, only a main portion of the semiconductor pellet 101 is bonded to the wiring substrate 104 by using a minimum necessary amount of resin 108. Thereby, it becomes possible to reduce the external size of the semiconductor device.
As a semiconductor device of this kind, there is proposed a semiconductor device which has still higher mount density. In such semiconductor device, for example, electrodes are further formed on the other of the main surfaces of the semiconductor pellet 101, and another semiconductor pellet is coupled to the electrodes. Alternatively, another semiconductor pellet is mounted on the surface of the wiring substrate 104 on which surface the solder balls 109 are formed.
In the conventional semiconductor device, coefficients of thermal expansion differ largely among the semiconductor pellet 101, the wiring substrate 104 and the resin 108. Therefore, at a high temperature, the wiring substrate 104 warps due to the bimetal effect. Thus, stress concentrates into coupling portions of the electrodes 103 and 106, so that there is a possibility that the projected electrodes 103 peel off from the joined interface portion of the electrodes 103 and the electrodes 106, or the projected electrodes 103 peel off from the semiconductor substrate 102. Therefore, there is a possibility that electrical connection between the semiconductor pellet 101 and the wiring substrate 104 is damaged. In order to avoid such disadvantages, in the resin 108, filler such as silica, alumina and the like which has a thermal expansion coefficient close to that of the semiconductor pellet 101 is dispersed within base resin such as epoxy resin and the like. Thereby, a thermal expansion coefficient of the base resin is lowered, and the effect of difference of the thermal expansion coefficients between the semiconductor pellet 101 and the wiring substrate 104 is reduced.
As an insulating substrate 105 used in the wiring substrate 104, an insulating board is generally known which is fabricated by impregnating resin into a laminated glass fabric body and curing the resin. The laminated glass fabric body are fabricated by stacking a plurality of glass fabrics each of which is made by weaving glass fibers into a cloth.
Also, in each of Japanese patent laid-open publication No. 6-204632 (hereafter referred to as prior art 1) and Japanese patent laid-open publication No. 7-112506 (hereafter referred to as prior art 2), there is disclosed a metal-clad laminated board for a printed circuit board. In the metal-clad laminated board disclosed in these publications, a surface resin layer having a low modulus of elasticity is disposed between a substrate layer of glass fabrics impregnated with epoxy resin and a metal layer formed on a surface of the metal-clad laminated board. Therefore, even when a temperature of the environment in which the metal-clad laminated board is used becomes high and the difference of thermal expansion coefficients between a wiring substrate and surface mounted devices becomes large, the surface resin layer which is in a rubber-like state deforms and a stress caused by the difference of the thermal expansion coefficients between the surface mounted devices and the wiring substrate is mitigated. Therefore, it is possible to prevent a stress from occurring in the solder coupling portions between the surface mounted devices and the wiring substrate.
Here, the inventor of the present invention considered on the case a semiconductor device shown in FIG. 3 is fabricated by using the wiring substrate disclosed in the prior art 1 and prior art 2, and found the following fact.
As a method of coupling the projected electrodes 103 and the pad electrodes 106, it is considered possible to form the projected electrodes 103 by using solder balls and to couple the projected electrodes 103 and the pad electrodes 106 by melting the solder balls. In this case, even if the wiring substrate 104 is heated when coupling the electrodes 103 and 106, there occurs no problem. However, as another method of coupling the electrodes 103 and 106, it is considered possible to heat superposed portions of the projected electrodes 103 and pad electrodes 106 and at the same time to press the projected electrodes 103 onto the pad electrodes 106, thereby thermal compression bonding between the projected electrodes 103 and the pad electrodes 106. In this case, since the surface resin layer of the insulating substrate 105 becomes rubber-like state, the pressed projected electrodes 103 together with the pad electrodes 106 are plunged or pushed into the insulating substrate 105.
The above-mentioned plunging of the projected electrodes 103 into the insulating substrate 105 becomes large especially when the projected electrodes 103 are fabricated in the following manner. That is, a metal ball is formed at the tip portion of a metal wire which is threaded through a capillary. This metal ball is contacted to the surface of the semiconductor substrate 102. Then, the metal ball is pressed and crushed by the lower end of the capillary. Thereafter, the metal wire is cut by pulling it while a portion of the metal wire near the crushed metal ball is left with the crushed metal ball. FIG. 4 shows a conceptual cross sectional view of a projected electrode 103 fabricated in this way. The projected electrode 103 shown in FIG. 4 has different diameters between a base portion 103a and an elongated portion 103b. That is, the diameter of the elongated portion 103b is smaller that of the base portion 103a. Also, the tip portion of the projected electrode 103 has a rotated parabola shape. Therefore, when the projected electrode 103 and the pad electrode 106 are thermal compression bonded, compressive force concentrates in the tip portion of the projected electrode 103. Thus, plunging of the projected electrode 103 into the insulating substrate 105 becomes large.
For example, in the projected electrode 103 fabricated by using a gold wire 25 xcexcm in diameter, the base portion 103a has a diameter of approximately 80 xcexcm, the elongated portion 103b has a diameter of approximately 25 xcexcm, and the height of the projected electrode 103 becomes approximately 75 xcexcm.
When the tip portion of the projected electrode 103 having such shape and size is superposed and pressed onto the pad electrode 106, the elongated portion 103b is compressed in the axial or vertical direction and expands in the radial or horizontal direction. Therefore, the height of the projected electrode 103 becomes lower. In this case, since the tip portion of the elongated portion 103b of the projected electrode 103 is thin, the pressing force by the projected electrode 103 concentrates on a small area of the pad electrode 106.
In the metal-clad laminated board disclosed in the prior art 2, the thickness of the surface resin layer having a low modulus of elasticity is equal to or larger than 20 xcexcm.
When the projected electrode 103 having an initial height of 75 xcexcm is pressed onto the surface of the wiring substrate 104 which is heated and softened, the surface of the pad electrode 106, and the tip portion of the projected electrode 103, is pushed down or plunged by, for example, 5-15 xcexcm from the initial location of the pad electrode 106.
Since the depth to which the projected electrode 103 is pushed down is relatively smaller than the thickness of the surface resin layer, it is generally considered that the depth to which the projected electrode 103 is pushed down becomes constant for every projected electrode 103. However, the inventor of this invention has found that the depth of each dent of the pad electrode 106 does not always become uniform.
The surface of the wiring substrate 104 is flat. However, the glass fabrics within the wiring substrate 104 are woven by glass fiber yarns each made of a plurality of glass fibers. Therefore, although not shown in the drawing, there are minute unevenness at the surface of each glass fabric. For example, in the glass fabric woven by using the glass fiber yarns which are made by bundling several tens through several hundreds glass fibers each having a diameter of 5 xcexcm, unevenness appears whose depth is, for example, 10-30 xcexcm and whose repetition cycle is, for example, 500-1000 xcexcm. It has been found that, by such unevenness at the surface of the glass fabrics, the depth to which each of the projected electrodes 103 is pushed down varies depending on the location on the wiring substrate 104.
FIG. 5 is an enlarged cross sectional view of a portion near the projected electrodes 103, and shows a condition in which the tip portions of the projected electrodes 103 together with the pad electrodes 106 are pushed down into the insulating substrate 105. As shown in FIG. 5, the height or level and/or the slope of the pad electrode 106 differs for each pad electrode 106. Also, the projected electrodes 103 tend to lean differently. As a result, the depth to which the projected electrodes 103 are pushed down vary depending on the location. Thus, condition of coupling between the projected electrodes 103 and the pad electrodes 106 vary depending on the location. The inventor has also found that such phenomenon occurs when the surface resin layer is made of other resin material such as epoxy and the like.
In general, the semiconductor pellet 101 and the wiring substrate 104 are mechanically joined by the resin 108 to strengthen the electric coupling by pressure welding, thermal compression bonding or ultrasonic bonding. Therefore, the above-mentioned uneven coupling condition between the projected electrodes 103 and the pad electrodes 106 does not always affect a quality of the semiconductor device. However, when the semiconductor device is used, for example, in an environment in which temperature varies remarkably, there is a possibility that reliability of the semiconductor device is deteriorated. Also, there is a possibility that an yield of manufacturing a semiconductor device is deteriorated and a cost of manufacturing a semiconductor device becomes high.
Therefore, it is an object of the present invention to obviate the above-mentioned disadvantages of the conventional semiconductor device and manufacturing method.
It is another object of the present invention to provide a semiconductor device and a method of manufacturing the semiconductor device in which reliable and stable electrical connection can be performed.
It is still another object of the present invention to provide a semiconductor device having high reliability and to provide a method of manufacturing such semiconductor device.
It is still another object of the present invention to provide a semiconductor device and a method of manufacturing the semiconductor device in which depth of cave-in of pad electrodes into pad electrodes of a wiring substrate can be uniformalized within a semiconductor pellet.
It is still another object of the present invention to provide a semiconductor device and a method of manufacturing the semiconductor device in which reliable electrical connection between projected electrodes of a semiconductor pellet and pad electrodes of a wiring substrate can be maintained within a semiconductor pellet.
It is still another object of the present invention to provide a semiconductor device and a method of manufacturing the semiconductor device in which an yield of manufacturing and a cost of manufacturing the semiconductor device can be improved.
According to an aspect of the present invention, there is provided a semiconductor device comprising: a wiring substrate which has a laminated glass fabric body made by laminating a plurality of glass fabrics and impregnating with resin, a resin layer on at least one of surfaces of the laminated glass fabric body, and a plurality of pad electrodes formed on the resin layer, wherein the resin layer has a thickness from 1.5 to 2.5 times the depth of unevenness of the surface of the laminated glass fabric body on which the resin layer exists; and a semiconductor pellet disposed on the wiring substrate and having a plurality of projected electrodes, the projected electrodes being electrically coupled to the pad electrodes by pressing the projected electrodes to the pad electrodes while heating the wiring substrate and/or the semiconductor pellet, tip portions of the projected electrodes together with the pad electrodes plunge into the resin layer.
In this case, it is preferable that the length of each of the projected electrodes before coupling with the pad electrode is larger than the thickness of the resin layer.
It is also preferable that, when the projected electrodes are pressed to the pad electrodes while heating the wiring substrate and/or the semiconductor pellet, the projected electrodes are compressed in a longitudinal direction and expand radially.
It is further preferable that the depth of plunging of each of the projected electrodes is 5-15 xcexcm.
It is advantageous that a pitch of disposition of the projected electrodes is sufficiently smaller than a repetition cycle of the unevenness of the surface of the laminated glass fabric body on the side of the resin layer.
It is also advantageous that the depth of the unevenness of the surface of the laminated glass fabric body on the side of the resin layer is 10-30 xcexcm.
It is further advantageous that the repetition cycle of the unevenness of the surface of the laminated glass fabric body on the side of the resin layer is 500-1000 xcexcm.
It is preferable that material of the resin layer differs from that of the resin impregnated into the laminated glass fabric body.
It is also preferable that the resin layer comprises material having a predetermined low elastic modulus at least at a predetermined high temperature.
It is further preferable that material of the resin layer is the same as that of the resin impregnated into the laminated glass fabric body.
It is advantageous that material of the resin layer is epoxy resin.
According to another aspect of the present invention, there is provided a method of manufacturing a semiconductor device comprising: preparing a wiring substrate which has a laminated glass fabric body made by laminating a plurality of glass fabrics and impregnating with resin, a resin layer on at least one of surfaces of the laminated glass fabric body, and a plurality of pad electrodes formed on the resin layer, wherein the resin layer has a thickness from 1.5 to 2.5 times the depth of unevenness of the surface of the laminated glass fabric body on which the resin layer exists; preparing a semiconductor pellet having a plurality of projected electrodes; and disposing the semiconductor pellet on the wiring substrate and electrically coupling the projected electrodes to the pad electrodes by pressing the projected electrodes to the pad electrodes while heating the wiring substrate and/or the semiconductor pellet.
In this case, it is preferable that the preparing the wiring substrate comprises: laminating a plurality of glass fabrics, impregnating the plurality of glass fabrics with resin and curing the resin, thereby fabricating the laminated glass fabric body; and forming a resin layer on at least one of surfaces of the laminated glass fabric body, such that the resin layer has a thickness from 1.5 to 2.5 times the depth of unevenness of the surface of the laminated glass fabric body on which the resin layer exists.
It is also preferable that the preparing the wiring substrate further comprises forming a plurality of pad electrodes on the resin layer.
It is further preferable that wherein the resin layer comprises material having a predetermined low elastic modulus at least at a predetermined high temperature.
It is advantageous that the preparing the wiring substrate comprises: laminating a plurality of glass fabrics, impregnating the plurality of glass fabrics with resin and curing the resin, thereby fabricating the laminated glass fabric body; wherein the resin layer comprises the same material as that of the resin impregnated into the laminated glass fabric body, and is formed during the fabricating the laminated glass fabric body.
It is also advantageous that, in the electrically coupling the projected electrodes to the pad electrodes, tip portions of the projected electrodes together with the pad electrodes plunge into the resin layer.
It is further advantageous that the depth of plunging of each of the projected electrodes is 5-15 xcexcm.
It is preferable that, in the electrically coupling the projected electrodes to the pad electrodes, the projected electrodes are pressed to the pad electrodes and, thereby, the projected electrodes are compressed in a longitudinal direction and expand radially, and tip portions of the projected electrodes together with the pad electrodes plunge into the resin layer.
It is also preferable that, in the electrically coupling the projected electrodes to the pad electrodes, the projected electrodes and the pad electrodes are coupled by pressure welding, thermal compression bonding and/or ultrasonic bonding.